1. Field of the Invention
The present invention relates to a liquid crystal display device provided with a pixel electrode having in one pixel a reflective electrode reflecting outside light and a transmissive electrode transmitting light from a back light source, and a manufacturing method thereof.
2. Related Background Art
In a general liquid crystal display device, a thin film of liquid crystal is placed between two substrates. Each of the substrates has an electrode on the surface facing the liquid crystal film. The polarizers are placed on both sides of the substrates. In a transmissive liquid crystal display device, a backlight is positioned behind the substrates. Alignment treatment is provided on the substrate surfaces having the electrode. A liquid crystal having desirable director, the average direction of liquid crystal molecules, exhibits birefringence. Incident light coming from the backlight through the polarizer becomes elliptic polarized light due to the birefringence, and enters the polarizer on the opposite side. When applying voltage between the upper and lower electrodes, it rearranges the director to change the birefringence of the liquid crystal film, thereby changing the condition of the elliptic polarized light entering the polarizer on the opposite side. Electro-optical effect of changing intensity and spectrum of light passing through the liquid crystal display device is thus obtained.
There are two types of liquid crystal display devices: a transmissive liquid crystal display device displaying images with a backlight (rear light source) mounted at the back or side thereof, and a reflective liquid crystal display device displaying images by reflecting incoming ambient light on a reflector mounted to a substrate. The transmissive liquid crystal display device has the problem that displayed images are invisible under bright ambient light because display light is darker than the ambient light. On the other hand, the reflective liquid crystal display device has the problem of having significantly decreased visibility under dark ambient light.
In order to solve the above problems, a liquid crystal display device employing a semi-transmissive reflective film transmitting a portion of light while reflecting another portion of light, which will be referred to hereinafter as a semi-transmissive liquid crystal display device, has been proposed. The semi-transmissive liquid crystal display device is disclosed in Japanese Patent Application Laid-Open No. H07-333598, No. 2000-19563, and No. 2000-305110, for example.
However, the conventional semi-transmissive liquid crystal display devices disclosed in the above applications have problems of complicated manufacturing processes and low manufacturing yields.
The present invention has been accomplished to solve the above problems and an object of the present invention is thus to provide a liquid crystal display device manufactured in simple processes while having high manufacturing yields, and a method of manufacturing the same.
A liquid crystal display device according to the present invention is a liquid crystal display device provided with liquid crystal material sealed between substrates and having a pixel electrode in a pixel on one of the substrates, the pixel electrode having a reflective electrode (for example, third metal thin films 10 and 11 in the following preferred embodiment of the invention) for reflecting light from outside, a transmissive electrode (for example, a conductive thin film 9 in the preferred embodiment of the invention) for transmitting light from a back light source, wherein the reflective electrode and the transmissive electrode are laminated with no insulating layers interposed therebetween. The liquid crystal display devices having the above configuration is easy to manufacture and produces high manufacturing yields.
The reflective electrode is preferably formed at a top layer directly under an alignment layer. It is also preferable to configure the reflective electrode by forming a conductive material to cover the reflective electrode before pattern formation, and removing the conductive material after the pattern formation, in order to prevent erosion of the transmissive electrode.
In a preferred embodiment, material of the reflective electrode includes aluminum, and material of the conductive material includes one of chromium, molybdenum, tantalum, and tungsten.
It is also preferable that a part of the transmissive electrode is removed at a connection between the transmissive electrode and the first metal thin film, and/or at a connection between the transmissive electrode and the second metal thin film, and the part is covered with the reflective electrode, so that the reflective electrode is connected to the first metal thin film and/or the second metal thin film. The configuration reduces connection resistance between the transmissive electrode and the first or second metal thin film.
Further, a periphery of the transmissive electrode in a pixel is preferably covered with the reflective electrode for stronger adhesion.
It is also preferable that the transmissive electrode has a concavity in a pixel and inner side portion of the concavity is covered with the reflective electrode.
More preferably, the overlap of the reflective electrode with the inner side portion of the concavity on the transmissive electrode in the pixel is 2 xcexcm to 6 xcexcm.
Besides, it is preferable in the pixel that a semiconductor film of a thin film transistor (TFT) section extends to a lower part of a source line.
On the other hand, a manufacturing method of a liquid crystal display device according to the present invention is a manufacturing method of a liquid crystal display device provided with liquid crystal material sealed between substrates and having a pixel electrode in a pixel on one of the substrates, the pixel electrode having a reflective electrode for reflecting light from outside and a transmissive electrode for transmitting light from a back light source, the manufacturing method having a step of forming the transmissive electrode and a step of forming the reflective electrode on the transmissive electrode, with no insulating layers interposed therebetween. In this method, the liquid crystal display is easy to manufacture and produces high manufacturing yields.
It is preferable that the step of forming the reflective electrode includes a step of forming a conductive material to cover the reflective electrode before pattern formation, and a step of removing the conductive material after the pattern formation
In a preferred embodiment, material of the reflective electrode includes aluminum, and material of the conductive material includes one of chromium, molybdenum, tantalum, and tungsten.
Another manufacturing method of a liquid crystal display device according to the present invention is a manufacturing method of a liquid crystal display device provided with liquid crystal material sealed between substrates and having a pixel electrode in a pixel on one of the substrates, the pixel electrode having a reflective electrode for reflecting light from outside and a transmissive electrode for transmitting light from a back light source, the manufacturing method having a step of forming and patterning the first metal thin film on an insulating substrate; a step of depositing the first insulation layer, a semiconductor active layer, an ohmic contact layer, and the second metal thin film; a step of forming a resist pattern by halftone exposure; and a step of patterning the semiconductor active layer, the ohmic contact layer, and the second metal thin film by etching. In this method, it is possible to decrease photographic processes to facilitate manufacture and attain high manufacturing yields.
It is preferable that the above method further has, after the step of patterning the semiconductor active layer, the ohmic contact layer, and the second metal thin film by etching, a step of forming the second insulation layer; a step of forming a uneven pattern by halftone exposure; and a step of patterning the first and second insulation layer by etching. In this method, it is possible to further decrease photographic processes to facilitate manufacture and attain high manufacturing yields.
Another manufacturing method of a liquid crystal display device according to the present invention is a manufacturing method of a liquid crystal display device provided with liquid crystal material sealed between substrates and having a pixel electrode in a pixel on one of the substrates, the pixel electrode having a reflective electrode for reflecting light from outside and a transmissive electrode for transmitting light from a back light source, the manufacturing method having a step of forming and patterning the first metal thin film on an insulating substrate; a step of depositing the first insulation layer, a semiconductor active layer, an ohmic contact layer, and the second metal thin film; a step of depositing the semiconductor active layer, the ohmic contact layer, and the second metal thin film; a step of forming a resist pattern by halftone exposure; and, after the step of patterning the semiconductor active layer, the ohmic contact layer, and the second metal thin film by etching, having a step of forming the second insulation layer; a step of forming a uneven pattern by halftone exposure; and a step of patterning the first and second insulation layers by etching. In this manufacturing method, it is possible to decrease photographic processes to facilitate manufacture and attain high manufacturing yields.
It is possible that the step of forming the transmissive electrode includes a step of forming amorphous indium tin oxide (ITO); a step of patterning the amorphous ITO; and a step of crystallizing the amorphous ITO. It is preferable in the step of crystallizing the amorphous ITO that the amorphous ITO is heated to 200xc2x0 C. or above for crystallization.
The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus are not to be considered as limiting the present invention.